I've not entirely written Keane off, altho I've said before that he played in a very different system at Burnley, similar to Ashley Williams at Swansea (both were asked to defend very deep - and do little more than defend and get forward for corners). Koeman wanted Keane (and Williams) further up the field and playing as more of a footballing centre back, which just isn't his game. Little wonder his confidence took a hit. I think it depends what we want him to be, tbh. Either way, I only have him and Holgate as our serviceable centre backs and while Holgate has looked promising, I don't have either as automatic 'must starts'. They're good as two of four, but I'd like to see two clear starters ahead of them both. Mori didn't improve in my books one bit - I'd have punted him to Spain or Italy in the summer gone and I hope we do the same at the next opportunity.
We simply can't miss out on a left back again tho. Much as Martina has grown on me (God loves a trier...) he shouldn't be the starting left back for any team with aspirations of top seven finishes. Ryan Bertrand, if Southampton drop, could well be worth a go.